Behavioral laterality in Yangtze finless porpoises (Neophocaena asiaeorientalis asiaeorientalis)

The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) is a critically endangered species with less than 1000 individuals expected to be left in the wild. While many studies have been conducted on laterality among several cetacean species, no studies investigating the Yangtze finless porpoise have been conducted. Using event sampling methods, several behaviors such as flipper-body touching, object touching, barrel-rolls, side swimming, and swimming direction were recorded from six captive porpoises (three males and three females). Analyses of 360 observations recorded over two months revealed that, at group level, porpoises showed laterality in swimming behaviors. Porpoises swam preferentially with their right pectoral fin upward and their left pectoral fin downward with a clockwise swimming direction and also displayed a consistent bias for a counterclockwise barrel-roll direction. No significant differences were reported for flipper use either during the interaction with conspecifics or with objects. The results from the current study provide novel insight into the cerebral asymmetry in a species previously ignored within the literature, thus improving our understanding on the extent of laterality in cetaceans and on the evolutionary history of hemispheric laterality for vertebrates in general.